title: Non-homologue pairing and spontaneous meiotic interchanges in Drosophila melanogaster females.
abstract: Spontaneous interchange between the X chromosomes and the C(2L) autosomal compound in their centromeric regions was studied in y/XY;C(2L);C(2R) and In(1)dl-49+BM1/XY;C(2L);C(2R) Drosophila melanogaster females. These females were mated with F(2L)/F(2L);C(2R) males. Interchange occurrence was recorded as the appearance of an F1 individual with a half-translocation of either X . 2L or Y . 2L type. 37 interchanges were recovered in y/XY and 67 in In(1)/XY females. The majority of the interchanges were of meiotic origin. The interchanges were mainly C(2L)-XY; the most frequent type of half-translocation was Y . 2L;dl-49+BM1. Inversion increased about 5-fold the interchange frequency. In the course of C(2L)-XY interchange, the other X chromosome and C(2R) compound regularly paired and disjoined. In y/XY females, 8 crossover half-translocations of meiotic origin were recovered. The results obtained indicate that meiotic pairing between the X's and C(2L) occurred in the females examined. According to our estimates, XY-C(2L) pairing is associated with interchange in the heterochromatic centromeric regions with a frequency of 10(-3). The recovery of crossover half-translocations supports the chromocentral model of non-homologous pairing and allows us to assume that a chromosome may simultaneously pair with a homologue and a non-homologue. The disjunction pattern of this trivalent depends on its structure in each particular case. The chromosome-segregation pattern resulting from spontaneous interchanges was similar to that resulting from radiation-induced interchanges in the immature oocytes described by Parker. This similarity suggests that non-homologue pairing occurs in the immature oocytes too. The non-homologue-pairing pattern established by the interchange test conformed well with that previously established in y/XY and In(1)XY females by the distribution test.
mesh_terms: D000818:Animals; D002875:Chromosomes / Q000648:ultrastructure*; D003433:Crosses, Genetic; D004331:Drosophila melanogaster / Q000235:genetics*; D005260:Female; D005838:Genotype; D007621:Karyotyping; D008540:Meiosis; D012730:Sex Chromosomes / Q000648:ultrastructure*; D014178:Translocation, Genetic; D014960:X Chromosome / Q000648:ultrastructure*